Brake beams are a component of the railroad car braking system. They transmit the translational motion and forces of the brake rods across the car and onto the brake shoes. The brake beam heads are a component of the brake beam that exert a force directly on the brake shoes. The brake heads must be positioned so that they exert a maximum force which is proportioned evenly along the brake shoes. Railroad freight car trucks are assembled in a loosely fitting manner, in order to easily accommodate manufacturing tolerances of parts and track irregularities. Therefore, railroad component manufacturers generally provide products which are easily assembled and which are not sensitive to imperfections in the fittings.
The unit guide wear plate is a device which fits inside the side frame of a railroad car proximate to the brake beam and the brake shoes. The function of the unit guide wear plate is to receive the brake beam end guide and to align its motion toward the wheels upon the application of the brake. For functional purposes the brake beam end guide must fit loosely within the unit guide wear plate. This requirement creates additional problems which need to be compensated in the design of components, such as the unit guide wear plate.
The brake beam end guide can travel approximately one inch between its retracted position and its braking position. Excessive looseness between brake beam end guides and their corresponding unit guide wear plates promote uneven wear of the brake shoes, the brake beam end guides, and the unit guide wear plates. This excess wear results in a costly and time consuming replacement process and creates burdensome maintenance problems for all railroad companies. Not only do the companies have to constantly replace the brake shoes, but there is also a costly need to repair and replace the brake beams themselves. With four brake beams and eight brake shoes per car, a substantial amount of repair is required of the railroad to maintain its fleet.
In general, the unit guide wear plates are the only means for guiding the motion of the brake beam end guide and for providing support against the effects of gravity. However, because the unit guide wear plate is required to loosely receive the brake beam end guide, the design of the current unit guide wear plates cannot accomplish this task without having the brake beam sag or droop. The drooping movement of the brake beam affects the nose of the brake beam and subjects the upper ends of the brake shoes to excessive wear. It also rotates the brake beam end guide within the unit guide wear plate such that additional pressure is exerted on the lower forward portion and the upper back portion of the brake beam end guide and the unit guide wear plate. This creates additional frictional resistance for the brake beam end guide and prevents the brake beam end guide from exerting a maximum pressure on the brake shoes and wheels. Thus, this defeats the purpose of having the brake beam end guide fit loosely within the wear plate, which is to provide compensation for the misalignment of other components of the braking system.
After a half million miles or so, the brake beam end guides and unit guide wear plates also wear significantly, thus requiring that the subject components be repaired or replaced. Continued operation under these conditions results in increasingly uneven brake shoe wear and diminished retraction of the brake beam end guide in the brake off position. Previous designs of the unit guide wear plate have attempted to solve these problems, but despite their efforts there still exists a need in the industry to adequately, economically, and efficiently resolve these problems.
U.S. Pat. No. 4,471,857, "Guide Bearing For Mounting Unit Brake Beams", by Murphy, contemplates solving some of these problems with a plastic wear plate design. However, in practice, this new design has not solved the drooping problem of the brake beam and has not created a component which is free from excessive wear. In fact, the plastic materials contemplated by this invention have exhibited a higher degree of wear than hardened steel designs. Furthermore, the brake beam end guides have not found a substantial coplaner cock free alignment in these new homes.
The Murphy patent also discloses an integral clip arm as part of the guide bearing wear plate. The effect of this clip arm has been to reduce the brake beam movement by a half an inch and in some cases prevent the application of the brake altogether.
In addition, to the problems created by the unwanted rotational movement of the brake beam, there exists an unwanted lateral movement of the brake beam which may cause unwanted wheel flange wear.
There have been past attempts to solve this problem by incorporating a spring inside the unit guide wear plate. However, given the dimensional constraints of the unit guide wear plate, these spring designs have been unable to fully react against the lateral force. Moreover, these spring designs have had a tendency to fail, causing the unit guide wear plate to crack and thereby, requiring replacement of the unit guide wear plate.
The nestling of the unit guide wear plate within the railroad freight car truck creates a difficult maintenance environment. In order to remove the unit guide wear plate, a series of heavy and burdensome parts must be lifted and set aside. The brake rigging must be disconnected, the side frames lifted and moved apart, the wheels rolled away and the brake beam itself must also be removed. Once the unit guide wear plate is removed and replaced the process must be reversed in order to reconnect the components. Therefore, there is a definite need in the railroad industry for long lasting, wear resistant, unit guide wear plates.
Current spring designs are created by a partial punch through an end wall of the wear plate. The spring has a tendency to break off at its anchoring point. In order to prevent the cracks from propagating into the remaining portion of the unit guide wear plate, two parallel holes are punched at the base of the spring. However, because manufacturing processes make it impossible to punch these holes exactly on a tangent, their net effect reduces the available spring force.
Therefore, there is a need to create a wear plate design which incorporates the concept of the spring component and which minimizes the failure of the spring and which also improves the spring rate. However, these new designs are generally limited to the confining dimensional requirements of the already existing components of the railroad car and braking system.
In addition, there is a need that such a design to be easily manufactured under current ,manufacturing processes without a burdensome increase in labor involved in manufacturing the wear plate.